1. Field of the Invention
The present invention relates to a method and apparatus for simultaneously detecting a size and concentration of an ionic material.
2. Description of the Related Art
Transistor-based biosensors are a kind of sensor for detecting ionic materials, especially, biomolecules, using electrical signals. Transistor-based biosensors are manufactured through semiconductor manufacturing processes and have the advantage of high speed electrical signal transition so that many studies involving them have been conducted.
U.S. Pat. No. 4,238,757 is the original patent relating to the detection of a biological response using a field effect transistor (“FET”). This patent relates to a biosensor detecting an antigen-antibody reaction by way of a current change of semiconductor inversion layer occurring due to a change in surface charge concentration. This patent relates to the detection of a protein among biomolecules.
The advantages of using a FET as a biosensor are lower costs, high-speed sensing and a simpler combination of integrated circuit (“IC”)/micro-electro mechanical systems (“MEMS”) process, compared to conventional methods.
On a surface of a gate electrode of a FET based biosensor, probe biomolecules may or may not be fixed. A detecting method for biomolecules using a FET-based biosensor involves a measuring current or voltage change due to the binding of a target biomolecule to the surface of the gate electrode to which probe biomolecules ma or may not be fixed. In an alternative method, the detecting method can be performed by measuring the current or voltage change due to the presence of a target biomolecule within a certain distance from a gate electrode to which no probe biomolecules are fixed.
However, when conventional FET-based biosensors are used to detect a target ionic material, the biosensors can detect only a concentration of unspecified ionic materials due to a voltage or current change, however, there is a problem in that it cannot be ascertained whether the target ionic materials is responsible for the voltage or current change.
When a primer is accurately selected and assay conditions are accurately set in order that a specific polymerase chain reaction (“PCR”) should be ideally performed in advance, the existence of target nucleic acid can be fully confirmed from only the existence of bands. However, when PCR is actually performed using an unknown sample, reactants obtained under second-best conditions instead of the optimum conditions are detected, and thus errors can frequently occur.
Therefore, there is a need for simultaneously measuring the concentration and size of ionic particles, for example, a length of nucleic acid, in order to determine whether an error has occurred or not.